The evolution of herbal medicine: behavioural perspectives

The current popularity of traditional herbal supplements, coupled with recent findings that add scientific legitimacy to the use of some medicinal herbs, prompts a question about the origins of herbal medicine in animals and ancestral humans. Medicinal herbs are used by animals and humans with the apparent prophylactic effects of reducing the likelihood or severity of illness from pathogens or parasites in the future. Medicinal herbs with anti-inflammatory, antimicrobial, immunomodulatory and/or analgesic properties are used in a therapeutic way to treat acute infections and inflammatory conditions, particularly in humans, and could have proven lifesaving to individuals living in nature. Was the origin of such types of herbal medicine the result of animals and humans learning that specific plant parts are effective for preventing or treating certain maladies, or was the origin a result of natural selection for a behavioural predisposition to seek out and use plant parts with particular physical or chemosensory markers of efficacy? Examining the predictions and requirements of both the learned and evolutionary explanations points primarily to an evolutionary model for the origin of herbal medicine that was expanded and enhanced by learning and social transmission. The evolutionary explanation accounts for the continued use of ineffective, as well as effective, medicinal herbs and the use of medicinal herbs with toxic effects. In animals one can point to origins of the practice of herbal medicine, as well as other behavioural defences against pathogens and parasites, as analogues of many aspects of modern human medicine and health care.